Exothermic welding has been widely employed in the formation of electrical connections or in the welding of steel such as rails and in joining reinforcing bar. The welding process utilizes powdered materials such as copper oxide and aluminum. The powdered material is placed in a crucible and ignited. Typically in electrical connections, the reduction of the copper oxide by aluminum produces molten copper and aluminum slag. Molten aluminum and molten iron can be made in similar fashion. The molten copper flows from the crucible over the parts to be welded contained in a mold, melting them and welding them together, forming a high quality low impedance connection. The slag forms on top and is removed. Such welding metals or powders, and a wide variety of molds and other related accessories are sold under the registered trademark CADWELD.RTM. by Erico Inc. of Solon, Ohio.
Most typically the molds are formed by two graphite blocks vertically split which are hollowed out to form the crucible, a receiving mold chamber for the pieces to be welded and interconnecting tap hole. The mold blocks are opened and closed by a toggle action handle frame or clamp which extends out to the side of the molds. Reference may be had to Burke U.S. Pat. Nos. 2,904,862 and 3,004,310 for illustrations of such exothermic cast welding mold assemblies. Where the mold parts are horizontally split, it is usual that the bottom of the block containing the crucible forms the top portion of the mold while the other or lower portion is hinged to separate from the top portion. The two mold blocks are also supported for opening and closing by a toggle clamp, again extending directly from the side of the mold blocks. The handles projecting laterally from the molds make the assemblies difficult to use in cramped quarters such as a narrow ditch where conductors for ground mats or other grounding systems, or cathodic protection connections, are often made.
Chain slings are typically used with mold assemblies for welding reinforcing bar such as shown in U.S. Pat. Nos. 3,234,603 and 3,255,498. In such patents the mold is in the form of a metal sleeve and separate molds are provided for the crucible and the tap hole or tundish, all of which may either be set one on top of the other or be held together by chain slings. The assembly and disassembly is time consuming, and more so in cramped quarters.
The molds are usually graphite or ceramic, and may be cleaned and reused. Properly handled, used and cleaned, molds may make fifty or more connections. However, improperly used or cleaned molds have to be replaced more often. Also, the molds have to be replaced or changed for different types of connections. There are literally dozens of types of connections and within each type of connection classification there are a wide number of conductor size variations. Also, the weld metal or powder is carefully pre-packaged by size. While the mold forming parts which receive the parts to be welded and which form the weld, need to be carefully designed and machined, that is not necessarily true of the crucible, and yet the crucible forms the largest portion of the mold system. Where the mold part and crucible are formed from a common block of graphite, excessive wear or damage to any part of the mold part requires that the whole thing be discarded even though the crucible is still usable. Accordingly it would be advantageous to have a system where the crucible was separate from the mold forming parts and the mold parts could be readily changed or substituted, while at the same time positioning the crucible and mold parts for quick and convenient cleaning for reuse.
If the crucible and mold are separable, it is important that when assembled they be held together with the proper degree of force so that no molten metal leakage occurs, and yet not too much force which might damage the mold parts, particularly if foreign matter is in the interface. It is also important that such force be quickly applicable or released, and readily adjustable.
It is also important that the jig or frame for holding the mold parts be low cost, able to separate and yet lock the mold parts quickly, and to hold the crucible for opening and closing travel with a mold part, and be properly held to such part so that no leakage occurs. It is also desirable that the crucible be easily removed and handled for convenient cleaning or preparation before assembly and clamping to the molds. In some situations, it may be desirable or even required to change crucibles. An example would be a crucible using a filter system for low emissions suitable for welding in confined spaces such as sold under the registered trademark EXOLON.RTM. by Erico, Inc.
It would also be important that the frame or clamp operate easily in tight quarters such as a ditch, and be self supporting. It would also be particularly advantageous if the frame or jig would partially open and hold the mold parts for insertion of the cable or parts to be welded, and fully open and hold the parts for cleaning. In cleaning a crucible, it is advantageous if a tool is inserted from the normally downwardly facing tap hole to knock any slag or residue out of the larger upper end of the crucible. In other words the crucible is best held inverted or upside down for cleaning.
Apparatus for making welds where two relatively thick conductors cross forms what is known as a lapped or cross connection. The molds for making this type of connection are complex, usually requiring two people to assemble for welding, and disassemble and clean. The molds comprise a bottom mold part forming part of the weld cavity and two vertically split molds forming both parts of the weld cavity and the crucible. Wear or damage to one part usually requires the whole assembly be replaced and a whole different set is required for each size.